What Can the Tsimane Teach Us About Heart Disease?

 
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The Tsimane are an indigenous tribal population living in the Bolivian Amazon. Their diet consists of about 2/3 starchy foods such as corn, manioc root, plantains, and rice, all of which they grow locally, and about 1/3 of foods they hunt and gather including fruit, nuts, freshwater fish, and animals. Only about 2% of their energy intake comes from foods they purchase in stores such as bread, pasta, crackers, and sugar. A study of Tsimane women who were breast-feeding found that their diet consisted of 72% carbohydrate, 14% fat, and 14% protein. The Tsimane do not consume any dairy products and eggs make up only about 0.5% of their calories. Their saturated fat intake averages only about 10.6g per day or only about 4% of total energy intake. Their intake of salt is also quite low compared to that seen in modern societies, and the Tsimane do not smoke.[1]

What is remarkable about the Tsimane is that they have the lowest reported levels of coronary artery disease (CAD) of any population studied to date. In the cross-sectional cohort study, researchers took CT scans of the hearts of 705 Tsimane between the ages of 40 and 94 years to measure the extent of the calcification of their coronary arteries. Based on the CT scans, 85% of the Tsimane people had zero CAC scores indicating no evidence of advanced CAD, another 13% had low risk (<100) and only 3% of Tsimane had a moderate to high risk CAC score of more than 100. These findings continued into old age, where 65% of those over 75 years old had a zero CAC score and only 8% had a moderate or high risk CAC score of more than 100. By comparison, a U.S. study of 6,814 people aged 45 to 84 found that only 14% of Americans had a CAC score of zero and 50% had a moderate to high risk CAC score (>100). "These findings are very significant," said Randall Thompson, MD, FACC, from Saint Luke's Mid America Heart Institute cardiologist, who presented the results of the study at the American College of Cardiology 2017 meeting. "Put another way, the arteries of the Tsimane are 25-30 years younger than the arteries of sedentary urbanites. The data also show that the Tsimane arteries are aging at a much slower rate."

In some ways the very low incidence of CAD among the Tsimane is not all that surprising. It has long been known that atherosclerotic disease progresses with age based on a variety of known and suspected risk factors. It is known to progress far more rapidly in those who smoke, have high LDL-cholesterol, high blood pressure, are physically inactive, and/or are overweight – especially if their weight gain leads to insulin resistance and diabetes. Compared to Americans and other modern people, the Tsimane have far lower blood pressure, cholesterol levels, and almost no insulin resistance and type 2 diabetes. So their low intake of salt, saturated fat, and refined carbohydrates coupled with high activity levels means that their lifestyle is likely largely responsible for their relatively far healthier arteries than people in modern societies. The LDL-C level of middle-aged and older Tsimane has averaged between 70 to 90mg/dl over the past 10 years. Their average blood pressure has been about 116/73mmHg and has remained normal even in people age 75 and older. By contrast, well over half of all Americans develop hypertension by the time they are 65 and more than 75% have hypertension at age 75 and above. The Tsimane spend only 10 percent of their daytime being inactive, instead spending most of their days participating in hunting, gathering, fishing, and farming. It should also be noted that the Tsimane do have a couple of fairly well-established CVD risk factors. About half have low HDL-C (<40mg/dl) levels, although there is growing evidence that lower HDL-C levels may not be as important as the functionality of the HDL particles. On average, the Tsimane have fairly high levels of the inflammatory marker hs-CRP, which has been established a fairly potent independent CVD risk factor. However, in the case of the Tsimane, the high hs-CRP levels may be due more to infectious diseases and parasitic infections and may not be coming from inflamed artery walls.[2]

The fact that the Tsimane have elevated hs-CRP and very low CAC scores casts doubt on the suggestion of some prior researchers who hypothesized that the relatively high levels of coronary artery calcium deposits in the mummified remains of four diverse human populations suggested chronic inflammation and aging were more important than traditional CVD risk factors. They noted the remains of Egyptian mummies, who like the Tsimane had high levels of infectious disease including a high prevalence of parasitic infections, were evidence that inflammation and aging rather than diet was the main cause of atherosclerosis. These same researchers noted that the mummified remains of ancient Native Americans, Aleutian Islanders, and Peruvian Indians also showed higher levels of calcified lesions than most modern people. While we do not know what their other CVD risk factors were, there is little doubt these ancient people had a high prevalence of infectious diseases and probably most had elevated hsCRP levels and inflammation. Based on these observations the researchers stated: "Our finding that atherosclerosis is common in four diverse populations is consistent with the hypothesis that atherosclerosis is indeed fundamental to aging." They concluded, "A chronic inflammatory burden may have played a greater role in ancient cultures than previously appreciated.[3] However, it is likely that all these ancient people consumed diets much higher in saturated fat, cholesterol, and/or salt than the Tsimane do today. The fact that 2/3 of the Tsimane age 75 and older still had a zero CAC score suggests that traditional CVD risk factors, rather than chronic inflammation and old age, are the main drivers of atherosclerotic disease.

Bottom Line: "This study shows that prevention really works," said Gregory S. Thomas, MD, who headed the Tsimane study. "Most of the Tsimane are able to live their entire life without developing any [clinically significant] coronary atherosclerosis. This has never been seen in any prior research. While difficult to achieve in the industrialized world, we can adopt some aspects of their lifestyle to forestall a condition we thought would eventually affect almost all of us." Drs. Kaplan and Thomas et. al. conclude: "These findings suggest that coronary atherosclerosis can be avoided in most people by achieving a lifetime very low LDL, low blood pressure, low glucose, normal BMI, no smoking, and plenty of physical activity."

By James J. Kenney, PhD, FACN

References:

[1] Martin MA, Lassek WD, Gaukin SJC, et. al. Fatty acid composition in the mature milk of Bolivian forager-horticulturalists: controlled comparison with a US sample. Matern Child Nutr. July 2012: doi:10.1111/j.1740-8709.2012.00412.x.

[2] Kaplan H, Thompson BC, Trumble BC, et. al. Coronary atherosclerosis in indigenous South American Tsimane: a cross-sectional cohort study. Lancet. 2017: http://dx.doi.org/10.1016/S0140-6736(17)30752-3.

[3] Clarke EM, Thompson RC, Allam AH, et. al. Is atherosclerosis fundamental to human aging? Lessons from ancient mummies. J Cardiol. 2014;329-34.

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